Traditional direct-write electron-beam exposure systems use an electron source substantially in the form of a point source. In these systems, typically, a minimum cross-section electron beam, produced from a point source, is deflected so as to scan across the surface of a sample. The deflected beam writes a pattern on the surface of the sample in a single, continuous stroke. Such systems are not practical for use in high-volume production of integrated circuits, because the throughput rate is too low.
To improve the throughput rate, multi-column type electron-beam exposure systems have been proposed by, for example, Chang, et al., in "Arrayed Miniature Electron Beam Columns for High Throughput Sub-100 nm Lithography," J. Vac. Sci. Technol. B 10:2743-2748, November/December 1992. In this proposal, it is asserted that, at a line width of 100 nm, a throughput rate of fifty 200-mm wafers (60 chips each) per hour or more could be achieved if 10 columns (each including an electron source, lens and deflector) are provided for every 20 mm.times.20 mm chip.
In a multiple-column type electron-beam exposure system, numerous columns are required. The inter-column distance, however, likely cannot be made as close as asserted in Chang, et al., because of the space requirements of the individual lenses and deflectors for each column. A very high throughput rate (as predicted on the assumption of 10 columns per 20-mm chip) would thus not be anticipated.